The present invention generally relates to a measuring system and method for detecting an object distance, and more particularly, to a measuring system and method for detecting an object distance using more than one of the transmitted media with different wave velocities, respectively.
The use of automatic measuring systems has become increasingly important with the rapid development of industrial techniques. For example, to avoid collisions, drivers must carefully park cars in parking spaces and an automated guided vehicle (AGV) transports goods to suitable position to keep away from obstacles.
U.S. Pat. No. 4,500,977 discloses xe2x80x9ca method and apparatus for measuring a distance using ultrasonic echo signals, particularly for use on a motor vehiclexe2x80x9d to detect and show the distance between vehicle and obstacles. Additionally, U.S. Pat. No. 4,015,232 discloses xe2x80x9cUltrasonic distance detector for vehiclesxe2x80x9d. The ultrasonic distance detector for vehicles uses a plurality of transducers located around the sides of the vehicle. Each of the transducers is connected to a receiver for detecting sonic echoes from too close objects. The output of each receiver is connected to individual indicator lamps and if any of the lamps are energized, the driver is warned that a part of the vehicle is in danger of a collision.
Particularly, a space position system has to detect a distance of the articles to locate precisely and quickly the objects. Conventionally, the measuring system uses ultrasonic waves as measuring media in the air and detects the object distance by reflective ultrasonic waves. FIG. 1 shows a reflective measuring system using ultrasonic waves in the prior art.
The conventional measuring system using reflective ultrasonic waves usually has an ultrasonic transducer-transmitted 100, an ultrasonic transducer-received 102, an object 104 and a peripheral circuit (not shown). The ultrasonic transducer-transmitted 100 and the ultrasonic transducer-received 102 are connected to the peripheral circuit. There is a distance between the object 104 and the ultrasonic transducer-transmitted 100 and the ultrasonic transducer-received 102.
During an operation, incident sound waves 106 generated by the ultrasonic transducer-transmitted 100 are partially reflected off the surface of the object 104. A portion 106a of the reflected sound waves is received by the ultrasonic transducer-received 102 and another portion 106b of the incident sound waves 106 form reflected sound waves 106b in the air due to obstructive articles 108 in the environment. Also, the reflected sound waves 106b are often reflected to the transducer-received 102. Afterwards, the incident sound waves 106 are formed by the ultrasonic transducer-transmitted 100 and processed by the peripheral circuit to compute the distance between the object 104 and the ultrasonic transducer-transmitted 100. However, the effect of the reflected waves of the obstructive articles 108 is totally ignored.
A conventional measuring system with reflective ultrasonic waves uses a principle, 2L=Txc3x97V. L is a measurement distance between the object 104 and the ultrasonic transducer-transmitted 100, T is the time for transmission of ultrasonic waves from the ultrasonic transducer-transmitted 100 to ultrasonic transducer-received 102, and V is the velocity of the sound waves.
The conventional measuring system has many disadvantages. For example, during measurement, many obstacles 108 other than the desired object 104 interfere with the sound wave reflections so that the ultrasonic transducer-received 102 receives reflective sound waves 106b resulting from the desired object 104 and the obstacles 108. If the obstacles 108 are closer to the ultrasonic transducer than to the desired object 104, the ultrasonic transducer-received 102 acquires instantly the reflective sound waves 106b from the obstacles 108. Therefore, the sound waves 106a reflected from the object 104 interfere with those of the obstacles, resulting in an imprecise measurement of object distance.
U.S. Pat. No. 6,166,995 discloses xe2x80x9cApparatus for distance measurement by means of ultrasoundxe2x80x9d that the ultrasonic pulses from respective ultrasonic transducers are superimposed on each other when no obstacle is detected during sequentially propagating ultrasonic pulses. In addition, U.S. Pat. No. 5,508,974 describes xe2x80x9cMethod and device for ultrasonic distance measuring.xe2x80x9d In a device for measuring the distance to an obstacle, a second transmission pulse as a control measurement for an ultrasonic distance measurement is transmitted only when an echo signal has been received for a first transmission pulse. Further, a timing window, within which the expected echo signal falls when it is reflected by an obstacle, is created.
Specifically, when positioned in an open space, the object 104 is difficult to measure since the geometric shapes of the object 104 is irregular due to an uncertain transmission time of the sound waves resulting in a poor computation precision for the peripheral circuit. Moreover, the intensity of the ultrasonic waves is inversely proportional to a distance away from the ultrasonic transducer-transmitted 100 in the air when a reflective measuring system is used for distance measurement. As a result, the signal/noise (S/N) ratio of the reflective ultrasonic detecting system is severely degraded, which leads to a poor measurement precision.
Furthermore, the transmission distance of the ultrasonic waves is at least double distance comparative to the distance between the object 104 and the ultrasonic transducer-transmitted 100. Even with the irregular surface of the object 104, the transmission distance of the sound waves is much higher than the object distance leading to poor measurement efficiency. U.S. Pat. No. 5,418,758 discloses xe2x80x9cDistance measurement systemxe2x80x9d utilized two reflectors mounted in different positions, respectively to receive reflected signals. U.S. Pat. No. 5,140,859 describes xe2x80x9cLong range ultrasonic distance measuring systemxe2x80x9d that two transducers are placed different locations. A pulse signal is generated by the master transceiver, which requires a time period of t1 to travel to the slave transceiver. After a time delay of t2 upon the receipt of the pulse signal by the slave transceiver it transmits a response signal back to the master transceiver. The response signal requires the same time period of t1 to be received by the master transceiver. The distance between the master transceiver and the slave transceiver is determined by an equation of 2xc3x97t1+t2.
Consequently, how to eliminate the interference with the reflective sound waves is a problem and how to reduce the transmission length of the sound waves for the measuring system manufacturers is currently a main issue.
One object of the present invention is to utilize a measuring system and method of detecting an object distance using a plurality of transmitted media with different wave velocities including light-speed waves (infrared rays or radio waves) and sound waves (ultrasonic waves). By simultaneously emitting the ultrasonic waves and infrared waves from a secondary detector to a primary detector and recording a time difference between the ultrasonic waves and the infrared waves, the object distance equal to the primary and secondary detector is obtained.
Another object of the present invention is to use a measuring system and method of detecting an object distance using transmitted media with different wave velocities including light-speed waves and sound-speed waves. The secondary detector is notified of the transmission of the light-speed waves and the sound-speed waves by using another light-speed waves so that the primary detector directly receives the sound-speed waves and light-speed waves from the secondary detector to compute a time difference between light-speed waves and sound-speed waves. Therefore, a reflective measuring system in the prior art is interfered with sound-speed waves from other obstacles for no purpose of distance measurement.
Still another object of the present invention is to use a measuring system and method of detecting an object distance using transmitted media with different wave velocities including light-speed waves and sound-speed waves. The light-speed medium serves as a communication media to establish a communication channel between the primary detector and the secondary detector. Such a communication channel can eliminate the unreasonable measurement result with errors to increase the measurement reliability.
According to the above objects, the present invention sets forth a measuring system and method of detecting an object distance using a plurality of transmitted media with different wave velocities. The measuring system has a computer, a primary detector and a secondary detector. The medium of transmitting a first signal and a second signal are preferably infrared waves with light-speed and ultrasonic waves with sound speed, respectively. The computer has a user interface to send a detection command to the primary detector by a communication interface (such as a serial port). Detecting results including a time difference and an object distance equal to the product of the time difference and the velocity of the first signal are displayed on the user interface of the computer. Since the velocity of the first signal is considerably higher than that of the second signal and a short transmission distance of the second signal (sound-speed wave), the transmission time of the first signal can be ignored but maintain a precise detecting.
In the present invention, the primary detector includes a serial communication device, a processing device, a sensor and a wireless communication device. The hardware structure of the secondary detector is typically similar to that of the primary detector except the serial communication device connected to the computer. Specifically, the communication device, the processing device and the sensor have many different functions on the basis of required measurement.
The primary detector mainly has a serial communication device, a first processing device, a first sensor and a wireless communication device. The primary detector is coupled to the computer by the serial communication device. The first processing device is coupled to the serial communication device, the first sensor and the wireless communication device, respectively. The primary detector transmits a signal-launching command responsive to the detection command of the computer by using the first sensor and the wireless communication device so that the first sensor simultaneously receives the first signal and the second signal. The first processing device is used to compute a time difference of the first signal and the second signal, respectively, sent to the first sensor. Therefore, a product, the object distance, of the velocity of the second signal in the first processing device and the time difference is obtained.
The secondary detector coupled to the primary detector has a second sensor, a wireless communication device and a second processing device. The second sensor and wireless communication is connected to the second processing device to serve as a message communication. The secondary detector is connected to the primary detector by the second sensor and wireless communication. When the secondary detector receives the signal-launching of the primary detector, the signal-launching is then sent to and identified by the second processing unit and. The second sensor and wireless communication thus asynchronously transmits the first signal and the second signal to the first sensor and wireless communication.
In the present invention, the measuring system for detecting an object distance utilizes a secondary detector to transmit ultrasonic waves to the primary detector. However, a measuring system in the prior art uses reflected ultrasonic waves subject to noise resulting from the reflection of objects. By contrast, in the present invention, a direct transmission and separate reception of the first signal and the second signal has advantageously a noise-resistant feature in the environment and a high signal/noise ratio (SNR).
During an operation of the measuring system, the computer sends a detection command to a primary detector through a communication interface. Afterwards, a signal-launching command is transmitted to a secondary detector by the primary detector to respond to the detection command of the computer. A first signal and a second signal are simultaneously emitted into the primary detector by the secondary detector to respond to the signal-launching command of the primary detector.
The first signal and the second signal are then respectively received from the secondary detector by using a first sensor of the primary detector and the velocity of the first signal is much higher than that of the second signal. The first processing device calculates the time difference of the first signal and the second signal sent to the first sensor of the primary detector to obtain an object distance equal to the product of the time difference and the velocity of the second signal. Finally, the object distance is read in the primary detector and displayed on the computer.
Since the velocity of the first signal is much higher than that of the second signal, the transmission time of the first signal can be ignored so that the time calculation of the primary detector and the secondary detector is deemed as simultaneous. Therefore, the time difference from the primary detector to the secondary detector is the transmission time of the sound-speed waves. Furthermore, the time when the second signal is reflected on the primary detector is much longer than that when the second signal is transmitted to the primary detector. As a result, the initial measurement of the light-speed waves and sound-speed waves which arrive at the primary detector is able to avoid the interference with the reflective waves of the first signal.
More importantly, in the same object distance measurement, the transmission length of the second signal is half of the object distance acquired by the reflected ultrasonic waves in the conventional measuring system. Namely, the object distance is equal to the transmission length of the second signal from the secondary detector to the primary detector. During transmission, the decay of the second signal is largely reduced to increase the signal/noise ratio in the same object distance measurement.
In summary, the present invention utilizes a measuring system and method of detecting an object distance using transmitted media with different wave velocities. The first signal and the second signal have advantageously a noise-resistant feature. Moreover, the transmission length of the second signal in the present invention is preferably half of the object distance acquired by the reflective ultrasonic waves in the prior art.